Kinetics and rat locomotor activity following cocaine and lidocaine administration

Cocaine abuse is a widespread problem in the USA. Illicit cocaine is usually never found in pure form but is adulterated with other agents, among which are the local anesthetics such as lidocaine. Adulteration of cocaine with another active agent allows the potential for various drug-drug interactions to occur. The presence of an additional active agent in illicit cocaine samples can complicate the pharmacological and toxicological responses elicited and possibly the mode of emergency medical care thereafter. When studying drug interactions, both the kinetic and dynamic aspects of each agent must be considered. This study investigated the plasma time course and tissue distribution of cocaine and lidocaine alone and in combination following a 5 mg kg(-1) intravenous injection in rats. The plasma time course of cocaine and lidocaine in combination did not differ from that seen when each drug was alone. Tissue contents were without change when administered alone or in combination at 5, 10 and 15 min following treatment. However, rats treated with cocaine and lidocaine in combination had significantly greater locomotor activity initially than animals treated with cocaine alone. The results suggest that cocaine and lidocaine interact on a pharmacodynamic basis without a change in the drug level of each agent.